60 THE PROTOZOA 



of the observations upon which they are founded, and that they 

 lack confirmatidn entirely.* 



3. Organs apparently of excretory function are present in many 

 Protozoa as the so-called " contractile vacuoles," one or more droplets 

 of clear liquid which make their appearance in the ectoplasm, grow 

 to a certain size, and then burst, emptying their contents to the 

 exterior. When the contractile vacuole reaches its full size, it often 

 bulges inwards far beyond the limits of the ectoplasm, and hence 

 may appear to lie in the endoplasm ; but its first appearance is 

 always in the ectoplasm, to which it strictly belongs. 



In non-corticate amoeboid forms the contractile vacuoles simply 

 empty themselves to the exterior, and the changing form of the 

 body does not parmit of determining whether the position of the 

 vacuole is a constant one. It is common in amoeba} for the vacuole 

 to be lodged in the region of the body which is hindmost in progres- 

 sion ; but this may be simply the mechanical consequence of the 

 streaming movements in the protoplasm, whereby the vacuole is 

 carried along to the hinder end of the body. In corticate forms, 

 on the other hand, the contractile vacuoles are constant both in 

 number and position, and void their contents through a definite 

 pore in the cuticle, directly or indirectly ; in many Flagellata and 

 Infusoria, for instance, the vacuoles do not discharge directly to 

 the exterior, but into the oesophagus or into a reservoir-vacuole 

 communicating with the oesophagus. 



The growth of the contractile vacuole is caused by fluid draining 

 into it from the body-protoplasm. In amoebae and forms of simple 

 structure no channels supplying the contractile vacuole are visible, 

 and it must be supposed to be fed by a process of diffusion through 

 the protoplasm from all parts of the body. In the highly-organized 

 ciliate Infusoria, however, the deepest layer of the ectoplasm has a 

 loose, spongy texture, and forms a definite excretory layer full of 

 spaces containing fluid, which drains into one or more main canals 



* It must be added further that, to judge from the figures left by Schaudinn 

 and published on Plate xxix. of his collected works (" Fritz Schaudinn's Arbei- 

 ten," Hamburg and Leipzig, 1911), the statements cited above appear to be 

 founded on preparations made by a method of technique which is recognized 

 generally as giving unsound cytological results namely, the method of dried 

 films stained by the Romanowsky stain. Schaudinn's statements are nevertheless 

 cited above on account of the numerous theoretical discussions and speculations 

 in modern protozoological and cytological literature of which they have been the 

 foundation. For my part, I disbelieve entirely in the theory that the flagcllum 

 represents a centrodesmose between two centrosomes , ' regard it as a simple 

 outgrowth from a blepharoplast of a nature essentially similar to the axapodium 

 of a Heliozoon. It is curious that no one has as yet extended Schaudinn's. theory 

 to the axopodia, the axial filament of which should also represent a centrodesmose, 

 if that view is correct for the axial filament of the flagellum, a view that seems 

 to me quite unthinkable from a phvlogenetic standpoint. Is it to be supposed 

 that the formation of each pseudopodium by a Heliozoon represents a rudimentary 

 mitosis ? 



